A value stream is all the actions required to bring a product or a service to a consumer. Value-stream mapping is a tool used to visualize and analyze the flow of materials and information in a value stream. Value-stream mapping identifies the sources of waste in a value stream and helps you improve the whole system, not just its individual components.

In Learning to See, Mike Rother and John Shook highlight the differences between "Push", which produces according to a schedule, and "Pull", which produces only what the next process needs when it needs it. They explain why "Push" results in overproduction and other types of waste and offer their guidelines on how to introduce a lean value stream that generates the shortest lead time, highest quality, and lowest cost:

Produce to your takt time. Takt time is the customer demand rate divided by available working time per day.

Develop continuous flow wherever possible. Continuous flow produces one piece at a time with each item passed immediately from one process to the next.

Use supermarket pull systems to control production where continuous flow does not extend upstream: for example, when a process has too much lead time.

Use a sized FIFO ("first in, first out") lane to maintain the flow when supermarket systems are not practical: for example, when we cannot create an inventory of all parts such as during custom development.

Try to send the customer schedule to only one production process. This process is called pacemaker: it sets a pace for all upstream processes and requires all downstream processes to be connected in a continuous flow.

Level the production mix: distribute the production of different products evenly over time at the pacemaker process.

Level the production volume: create an "initial pull" by releasing and withdrawing small, consistent increments of work at the pacemaker process. Consistent increment of work, aka "pitch" or "management time frame", will help you establish your takt time.

Develop the ability to make every part every day or every pitch in processes upstream of the pacemaker process.

The authors also included a list of questions designed to help you create future-state value-stream maps:

What is your takt time?

Will you build to a finished goods market from which the customer pulls, or directly to shipping?

Where can you use continuous flow processing?

Where will you use supermarket pull systems?

At what single point in the production chain will you schedule production?

How will you level the production mix?

What increment of work will you consistently release?

What process improvements will be necessary?

These questions along with two manufacturing plant examples will help you develop and introduce your own lean value streams in your organizations.

Learning to See is a well-written must-to-read technical workbook on value streams. I recommend it to anybody interested in Lean. Happy reading!